The present invention generally relates to the field of medical instruments for dissecting human and/or animal tissue.
Such an instrument is known, for example, under order numbers 651050, 651055, 651060 or 651065 from the German catalog “Endoskope und Instrumente für HNO” [Endoscopes and instruments for ENT], 6th edition, Janurary/2000, from Karl Storz GmbH & Co. KG.
The instrument for dissecting tissue is an instrument for detachment of tissue, for example of hard tissue and/or bone, in particular a tissue punch.
Surgical instruments of this kind are used in the context of minimally invasive surgery for detaching hard tissue or bone in the human or animal body, usually under endoscopic visual control. For this purpose, instruments of this kind have an elongate shaft at whose distal end at least one movable tool is arranged which interacts with another movable or immovable tool at the distal end of the shaft in order to detach tissue.
Surgical instruments whose tools cooperate with one another on the basis of an axial relative movement have the advantage that the effective diameter of the instrument does not change upon opening and closing of the tools. As a result, damage to the surrounding tissue or surrounding bone by opening and closing of the tools is avoided.
By virtue of the fact that the effective diameter of the instrument does not increase upon opening and closing of the tools, such instruments can also be used in smaller body apertures than can those instruments which have tools opening like forceps.
Such tissue punches are therefore preferably used in ear, nose and throat surgery (ENT surgery) in which the smaller effective diameter of the instrument is of great advantage.
Such instruments have a shaft at whose distal end two tools are arranged. Of these two tools, at least one is axially movable relative to the second tool. In the known instrument, at least one of these two tools has an approximately circular cutting element on the side facing toward the second tool. By means of their axial relative movement with respect to one another, the two tools act in the manner of a punch. In this case, the at least one cutting element defines a punch area which is approximately at right angles to the longitudinal axis of the shaft in the distal area thereof.
During use of these instruments, however, it has been shown that high loads can occur in small areas of the cutting elements of the instrument, especially when cutting through bone lamellae which are at an angle to the punch area. It has been found that this can lead to damage of the cutting surfaces or even to breaking-off of metal pieces from the cutting elements. These metal parts that have broken off are extremely sharp-edged and remain in the patient's body. These metal pieces left behind may migrate through the tissue and may cause not inconsiderable damage there. This is extremely dangerous for the patient, especially in the area of ENT surgery.
The operational safety of the known instruments is thus not guaranteed.
The patent specification U.S. Pat. No. 5,582,618 discloses a surgical instrument with a shaft at whose distal end two tools are arranged, of which one tool is axially displaceable relative to the second tool. These two tools each have a straight cutting element on an upper edge. A straight punch line is defined by these cutting elements.
The disadvantage of these instruments is that they only permit cutting along a straight punch line. Cutting about a partial circle, as is possible with the above-described instruments and as is desirable especially in ENT surgery, is not possible with such an instrument.
When an instrument of the type specified in the introduction is to be used for punching of bone lamellae, as is the case without limiting the general application of the instrument of the present invention, it is necessary first to push the distally arranged tools of the instrument through the bone lamella until the punch area comes to lie in the area of the bone lamella. The previously known instruments are not suitable for cutting through bone lamellae.